The present invention relates, in general, to electronic sensor circuits and, in particular, to a new and useful circuit for use in a fiber optic vortex shedding flow meter which utilizes the bending of a fiber optics fiber for determining the flow of a fluid.
Fiber optic vortex shedding flow meters are known which utilize a fiber that can transmit light which is connected between a light emitting device and a light detecting device. Bending in the fiber due to the passage of shedded vortices from an obstruction in a flow passage give a measurement of the flow rate.
Two-wire, 4 to 20 ma (milliamps) control transmitters are known and utilized as a standard mechanism for transmitting signals.
The electronics for a two-wire, 4-20 ma industrial control transmitter has only about 3.5 ma and 10 volts with which to operate. Fiber optic systems presently require several ma for the light emitter, often 200 ma or greater and as such are not compatible with two-wire, 4-20 ma transmitters.